There are two kinds of conventional optical coherence tomographies, time domain OCT and frequency domain OCT, in which dot scanning scheme is adopted using broadband light source and each needs more than one separate scanner. FIG. 1 shows schematic diagram of conventional time domain OCT and FIG. 2 shows that of conventional frequency domain OCT.
In time domain OCT as shown in FIG. 1, light beam coming from a broadband light source (12) is split by an optical splitter (30) into two light beams, which are incident on a reference mirror (50) and a subject and reflected from them, respectively. The reflected light beams are combined at the optical splitter (30), and the optical path length difference between the two light beams gives rise to interference signal (that is, interference pattern). The interference signal is detected by a photo diode (90) and is subject to A/D conversion and demodulation process, resulting in image signal in depth. To obtain two dimensional image, two scanning schemes by movements of both the reference mirror (50) and a scanner (80) have to be accomplished, which is referred as x-z scanning. However these two scanning schemes have difficulties in synchronizing the two movements, take long time in obtaining image, are susceptible to noises by movements of the subject and have low signal to noise ratio (SNR).
In frequency domain OCT as shown in FIG. 2, light beam coming from a broadband light source (12) is, as in the time domain OCT, split by the optical splitter (30) into two light beams, which are incident on the reference mirror (50) and the subject and reflected from them, respectively. The reflected light beams are combined at the optical splitter (30). The combined light beam is detected by a spectroscope (100) and Fourier transformed, resulting in image signal in depth. The frequency domain OCT does not need z-direction scanner and just uses x-direction scanner (80) to obtain two dimensional image. In the frequency domain OCT, higher signal to noise ratio can be obtained than in the time domain OCT. However the frequency domain OCT also have problems that the image is still affected noise by movements of the subject and the spectroscope (100) is to be implemented for detecting the light beam.